(1) A library of cDNAs made from differentiated mouse neuroblastoma mRNAs was found to contain at least four different clones whose fusion proteins had neurotrophic activity for rodent and chick neurons cultured from the central and peripheral nervous systems. (2) Three clones from this library appear to encode the angiotensin II (A II) receptor sequence, as determined by examination of the A II-induced ion flux through the membranes of oocytes injected with transcripts of these clones or by mRNAs hybrid-selected by them. (3) The transcript from another clone from this library appears to stimulate oocytes to bind Head Activating Peptide (HAP), an undecamer which is formed by neuroblastoma cells and may function as an autocrine regulator of cell growth. (4) Synthetic HAP was found to promote survival of cultured chick sympathetic cells with great potency, as did Triap (1.1.3-tricvano-2-amino-l- propene), which also was found to stimulate neurite formation and some enzyme activities in PC-12 cells. (5) The fusion protein of a cDNA clone (1-3) obtained from size-fractionated mRNAs from wounded cerebral cortex of the rat, proved to be a powerful trophic factor. (6) A clone from a rat hypothalamus library which bound one of two degenerate synthetic oligonucleotide probes for HAP was sequenced to reveal a sequence which did not code for HAP or any other known sequence. Other clones from neuroblastoma cells which bind these oligomers are being identified. (7) A project to obtain cDNA and genomic clones for the alpha-2 adrenergic receptor in rodents has been initiated.